1. Field of the Invention
The present invention relates to an image processing system of the type in which image data as read by an image reader is compressed, and stored into a memory of a large memory capacity, and the image data is repeatedly read out of the memory and is transferred to an image output terminal.
2. Discussion of the Related Art
RDH's (recirculating document handlers) are known in the art. In the conventional RDH, a set of original documents is repeatedly read by an automatic image reader, and a requested number of copies of the set of documents is produced. Therefore, when the number of copies is increased, the number of times the documents are handled is increased, and thus, the likelihood of damaging the documents is increased. An electronic RDH can produce the requested number of copies while handling the documents only one time. In the electronic RDH, a data storage unit is provided for storing the image data as it is read. The memory capacity of the storage unit is desirably large. For this reason, a magnetic memory device, such as a hard disk, is used. Of course, a semiconductor memory may also be used. To output a requested number of copies, a set of original documents is read one time in the presented order, and the image data is stored in the storage unit. The image data stored is repeatedly read out of the storage unit in the presented order, and transferred to the image output terminal. The image output terminal produces the requested number of copies.
Since the image data may contain a tremendous amount of information, the memory capacity of the storage unit must be extremely large in order to store the image information of a plurality of original documents. To solve this problem, the combination of a compressor and a decompressor is used to compress the data and then to decompress the compressed data. The compressor compresses the data to reduce the amount of image data to be stored into the storage unit. The image data read out of the storage unit is then decompressed into the original form. The decompressed data is transferred to the image output terminal.
In the magnetic memory device, such as a hard disk, an access time including a seek time and the like is approximately 1M byte/sec. A normal signal transfer time is 10M bytes/sec. Thus, a speed gap exists between the access time and the transfer time. To cope with the speed gap, a page buffer is provided. The compressed data from the compressor is temporarily stored into the page buffer for every page of the document. After the storage of the image data into the hard disk is completed, the data is read out of the hard disk into the page buffer for every page of the document. Then, it is sent to the decompressor. The decompressed image data is transferred to the image output terminal.
In the image processing system of the type in which the data is stored in the hard disk sequentially for every one page of data, through the page buffer, and then is read out of the disk, the time taken for the reading and writing of data from and to the disk impedes the copy output.
Editing commands, such as "cut and paste", masking, and "pickup and move", are difficult for the RDH, as described above to handle. The image data as read by the image reader is input to the control unit of the image processing system in a real time manner, and stored in a data storage unit. Therefore, the image data is read out of the storage unit and is used for the editing. Since the stored data is the compressed data, positional information in a coordinate system cannot be obtained from the compressed data. The same is true for image data rotation. For this reason, to perform editing, the compressed data must be read out of a storage unit and decompressed. The decompressed data is developed into bit map data, and loaded into a page buffer. To this end, a page buffer for editing must be additionally provided. This leads to an increase in the cost of manufacturing.